The present invention relates to a method for operating a web offset printing press.
A web offset printing press of this type prints and processes at least one material web, e.g., paper, and newsprint in particular, e.g., for a daily newspaper. To print, printing units and/or printing unit assemblies are provided, in which driven impression cylinders print material webs. “Processing” can refer, e.g., to perforating, or the subsequent cutting, folding, and assembling in a folder, and is also a component of web offset printing press according to the present invention. Further transport elements are also provided to transport the at least one material web through the web offset printing press into the at least one folder, which represents the end and completion of a particular production run. These further transport elements can be, e.g., drawing rollers in the superstructure upstream of the folders, merging drawing rollers in the folder, draw-in mechanisms, or reel changers. In general, “transport element” is intended to mean an element that guides and/or transports and/or directs the material web, and or that interacts with the material web, and/or stores the material web, e.g., stores it dynamically, or a reel changer, which contains, e.g., a paper roll with the rolled-up material web for use in production.
The inventive web offset printing press includes at least one folder, printing units and/or printing unit assemblies, and transport elements, which are electrically driven at least partially mechanically independently of each other. As a result, some or all of the elements/assemblies listed are not coupled with each other by a mechanically continuous shaft. Instead, they are electrically driven by several electrical drives (composed, e.g., of a driving unit and an electric motor) that operate mechanically independently of each other. During printing operation, the elements/assemblies listed are synchronized with an electronically generated synchronization clock using setpoint value assignments from at least one master axis.
The master axis can be, e.g., a kinematic reproduction of “virtual” mechanical shaft, which would mechanically couple the elements listed above. The synchronization clock can be generated and distributed in real time, both in terms of time and with regard for the accuracy of the position/motion setpoint value. The highly exact master axis signal, which can be composed, e.g., of position setpoint values, speed setpoint values, or other motion-relevant setpoint values in a temporally predetermined sequence, is preferably distributed via a real-time bus to the various elements and/or assemblies. This will be discussed in greater detail below.
A known method for web offset printing presses with one or more webs, with, e.g., individually driven printing units or printing unit assemblies, one or more individually driven folders, further processing stations, which are not described further, and individually driven drawing rollers in the superstructure upstream of the folders, individually driven merging drawing rollers in the folder, individually driven draw-in elements, individually driven reel changers, all individual drives on the webs that are transported into the same folder, are assigned to a “virtual production master axis”, so they can be followed in electronic angular-locked synchronization.
A virtual master axis is the position reference (φLA=position setpoint) for the assigned individual drives, which is calculated in a control system and moves in proportion with the desired machine speed. This position reference is transmitted to the drives simultaneously (synchronously) via rapid realtime bus systems and, optionally, via further, intermediately connected assembly control systems. The individual drives follow this position setpoint with the aid of their own digital position control. To adjust the angular position of the individual drives relative to the web that is passing through them, an individual angular offset Δφi is also calculated for each individual drive, and it is added to the current master axis position. The total position setpoint of an individual drive is therefore defined asφi=(φLA+Δφi)
The calculation of the individual values for the angular offset Δφi is carried out, e.g., in control station computers with knowledge of the selected web travel for production, and of the web paths covered between the individually driven processing stations. The transmission of the offset values is also carried out via a suitable data bus between the control stations and the control systems of the drive system.
For printing unit assemblies, the angular offset values of the drives is calculated such that color printing with precise register results, for driving the folder, e.g., an angular offset ΔφF, which brings the cutting cylinder into the desired position for the cutting register (position of the dividing cut at the start of a page).
Basically, the control system for the drives must move all individual drives at the processing stations into these positions in accordance with the angular offset values for the correct register. This takes place preferably before the start of production, to prevent waste (preset, default machine settings).
In the “Dezentralen Antriebssystem zur Synchronisierung von wellenlosen Druckmaschinen” [Decentralized Drive System for Synchronizing Shaftless Printing Presses] from Bosch Rexroth Electric Drives and Controls GmbH, this task is carried out automatically (by the drives) in the individual drives of the system via the “dynamic synchronization” function:
The drives move automatically—guided by the drives—based on a command, from any starting position into the target position=current master axis position+angular offset,φi=(φLA+Δφi).
For this procedure, it does not matter if the master axis φLA is still at a standstill, or if the master axis (and, therefore, the individual drives and the entire machine) is already in motion. To elucidate the basic process, FIG. 2 shows the speeds that occur during “dynamic synchronization”.
Whether and when during the course of preparation and start-up of a machine these motions for synchronization can be carried out is therefore not determined by the properties of the drive system, but rather by the special basic conditions and limitations of the processing process in the machine:
The printing units in the machine of the type described can be synchronized at any time, provided they are still in the “impression throw-off” position, i.e., the impression cylinder has not yet come in contact with the printing stock (web).
Publication DE 102 43 454 B4 makes known a method of the type described initially, which provides that the current actual value position of the folder is used as the starting value for the “virtual” master axis. The disadvantage is that practically the entire printing press can contain initial-motion setpoint values that are unfavorable and that deviate from the current position or the current condition of motion of many elements; in addition, a method of this type lacks flexibility and responsiveness, and is limited in terms of possible configurations, because it is designed for use with only one folder. With this method, the dynamic performance is also relatively inaccurate and very limited; the entire system of the web offset printing press that operates with this method—in accordance with the mechanical limitations of the folder—must therefore be started up very slowly, to prevent the web from tearing.
In addition, this method of setting the starting position can only be used when each of the webs—with the assigned printing units or printing unit assemblies—is conveyed into only one folder.
This method cannot be used in production situations in which, after the web is printed by one printing unit assembly, it is separated and transported to two different folders. According to the method described, the master axis position for this printing unit assembly can only be set to the position of a first folder. The second folder must then be synchronized with the target position of the production master axis—with its default settings—with addition of the calculated angular offset for its particular cutting register.